This invention relates to the control of light distribution and direction and, more particularly, to a lighting system that utilizes a self-luminous light source.
One type of self-luminous light source in use today comprises an axially elongated glass tube sealed at its ends, phosphor coated on its inner surface, and filled with a radioactive gas, such as tritium. When beta emission from the gas strikes the phosphor coating, visible light is emitted from the tube. Miniature self-luminous light sources of the described type are commonly used to backlight liquid crystal displays in digital watches and other electronic instruments with visual displays. In contrast to incandescent lamps, such a self-luminous light source requires no electrical power source, illuminates the liquid crystal display in the absence of ambient light without a switching operation, and provides many years of maintenance-free operation.
The common practice is to mount one or more miniature light sources, depending upon the area of the liquid crystal display to be illuminated, in a shallow pan having a light-reflective surface. The pan, which is located adjacent to the back face of the liquid crystal display, serves to hold the light source in place and reflect all the light emitted therefrom through the liquid crystal display. For digital watch applications in particular, the cross-section of the glass tube is elongated. The wider and thinner the cross-section of the glass tube, the more area of the liquid crystal display can be illuminated without increasing the thickness of the liquid crystal display-light source assembly. If the area of the liquid crystal display to be illuminated is wider than the light source to be used, the current practice is to use a plurality of light sources so the resultant area of the light sources coincides with or exceeds the area of the liquid crystal display to be illuminated.